Adult western corn rootworms on maize leaves © Stefan Töpfer, CABI
Crop rotation is often recommended as an effective control method against agricultural pests, including corn rootworms. Rotation works by removing the host on which the pest feeds and reproduces, and planting a crop which they are unable to live on. This reduces the number of pests that survive to the next season. Crop rotation is a common approach used to control the corn rootworm (Diabrotica virgifera virgifera) which, as you can probably guess, is a major pest of corn (Zea mays). These rootworms lay their eggs in corn fields, so that when the eggs hatch, the larvae can feed on the corn roots in the field. Rotating corn with soybean (Glycine max) means the farm remains productive in all seasons, while the soybean’s natural antiherbivory defences keep corn rootworm numbers low. This method saves the farmer money that could otherwise be lost through yield losses, the purchase of insecticides or the purchase of corn hybrids toxic to rootworms, which in total costs growers in the USA at least $1 billion per year.
In the past few years, however, growers practising crop rotation have seen an increase in the number of corn rootworms resistant to the rotation method. Scientists studying the corn rootworm have previously drawn a blank when trying to discover why some rootworms were more resistant. It’s only when they stopped looking at the organism itself that they found an explanation.
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